【作者】 冯光勇；

【导师】 张崇才；

【作者基本信息】 西华大学 ， 材料加工工程， 2008， 硕士

【摘要】 中、小型冷冲压模具工作时受到压缩、冲击、摩擦等机械力的作用,通常表现的失效形式为磨损、变形及断裂等,使用寿命较低,时常选用含较高合金元素的合金钢制造,热处理工艺比较复杂。针对这个问题,本文分析了冷冲压模具的工作条件,指出它的主要性能要求应是良好的耐磨性和足够的强韧性等,因而研究了T12钢和GCr15钢的渗硼工艺,对比研究了它们的常规球化退火,循环球化退火、以及屈氏体化处理和四步热处理的碳化物球化效果,进一步研究了渗硼+四步热处理的复合强化工艺及其组织与性能,分析了渗硼和钢的强韧化机理。根据试验结果和讨论分析,得到以下结论:（1）渗硼温度为850℃,渗硼时间由1h逐步增加到5h时,T12钢的渗层由40μm逐步增加到93μm;GCr15钢的渗层由20μm增加到53μm。这两种钢的渗层深度都随着渗硼时间的增加而增加,渗层厚度的增长速率呈先快后慢的趋势发展;在相同的时间内,T12钢的渗层深度始终高于GCr15钢。渗硼时间为5h,渗硼温度从750℃逐步升高到950℃时,T12钢渗硼层深度由50μm增加到163μm,GCr15钢渗硼层深度由32μm逐步增加到83μm;这两种钢的渗层深度都随着渗硼温度的增加而增加,渗硼层深度增加的速率也随温度升高而加快。（2）渗硼时间为5h时,温度由750℃逐步增加到900℃时,T12钢渗硼层的硬度由1155 HV_0.1逐渐增加到1216 HV_0.1,到950℃时又下降到1177 HV_0.1;GCr15钢渗硼层的硬度由1147 HV_0.1逐渐增加到1219 HV_0.1,到950℃时又下降到1163 HV_0.1。当温度为850℃时,渗硼时间在1h～5h范围内,T12钢渗硼层硬度在1178HV_0.1～1205HV_0.1范围内波动,GCr15钢渗硼层硬度在1150HV_0.1～1208HV_0.1范围内波动,表明渗硼时间对T12钢和GCr15钢的表层硬度值的影响较小。（3）T12渗硼后,其表面硬度为835HV_0.1,在次表层硬度达到1220HV_0.1,随渗层深度的增加,硬度逐步下降至基体硬度;GCr15也随渗层深度的增加,硬度逐步下降至基体硬度,它的渗层表面硬度为831HV_0.1,次表层的硬度达1211HV_0.1。（4）T12钢和GCr15钢的硼化物层与过渡区的交界十分平坦,其硼化物层与过渡层接触面很少,即硼化物针插入过渡区的厚度较浅（特别是GCr15钢）,因而削弱了与金属基体的结合力,这对渗硼层的剥落起到促进作用;另外,由于过渡层中存在着碳和硼的浓度梯度,导致过渡层是逐步地过度到心部基体组织的,这就造成了过渡层与基体组织之间没有明显的分界线,弥补了上述缺陷,即提高了渗层与金属基体的结合力,对克服渗层剥落起到有力的促进作用。（5）T12钢较好的渗硼工艺为900℃渗硼5h,其渗层厚度可以达到116μm,硬度能够达到1216 HV_0.1。GCr15钢较好的渗硼工艺为900℃渗硼5h,其渗层厚度可以达到67μm,硬度能够达到1219HV_0.1。（6）T12钢进行碳化物微细化工艺1（950℃高温固溶+700回火）处理后得到了良好的碳化物微细化效果,其中的碳化物细小、圆整、均匀分布;碳化物微细化工艺2（950℃高温固溶+760℃保温2小时+690℃保温3小时）的碳化物微细化效果次之,其中有部分尖角状碳化物存在;常规球化退火的碳化物球化效果较差,其中存在较多粗大、尖角状的碳化物。四步热处理和屈氏体化处理中的淬火回火工艺与常规的淬火回火工艺相同,都进行760℃加热淬火+150℃回火60min的处理,都得到回火马氏体+碳化物。其中,四步热处理后得到的碳化物最细小、圆整、分布最均匀,而屈氏体化热处理后存在部分粗大、尖角状碳化物,常规热处理后存在较多的粗大、尖角状碳化物。因此,T12钢四步热处理后的强韧性优于屈氏体化热处理,更优于常规热处理。（7）GCr15钢进行碳化物微细化工艺（950℃高温固溶+700℃高温回火）处理得到了良好的碳化物微细化效果,其中的碳化物细小、圆整、均匀分布;循环球化退火的碳化物微细化效果次之,其中有部分尖角状碳化物存在;常规球化退火的碳化物球化效果较差,其中存在较多粗大、尖角状的碳化物。四步热处理和循环球化退火后的淬火回火工艺与常规的淬火回火工艺相同,都进行840℃加热淬火+150℃回火60min的处理,都得到回火马氏体+碳化物,其中四步热处理后得到的碳化物最细小、圆整、分布最均匀,而循环球化退火+常规的淬火回火后存在部分粗大、尖角状碳化物,常规淬火回火后存在较多的粗大、尖角状碳化物。因此,GCr15钢经四步热处理后的强韧性优于循环球化退火后的淬火回火,更优于常规热处理。（8）T12钢经过复合强化热处理后具有以下特点:渗硼层厚度能达到120μm,显微硬度在1235HV_0.1左右;心部组织为回火马氏体加细小、圆整、均匀分布的碳化物,心部硬度达到61.5HRC;因而能满足中小型冷冲压模具对耐磨性和强韧性的要求。（9）T12钢的Acm为820℃,在900℃的温度下渗硼5h,渗碳体分解并进入奥氏体,经过5h的扩散,可以在较大程度上使碳原子扩散均匀并达到固溶效果,所以建议把固溶温度由950℃降到900℃左右。（10）GCr15钢经过复合强化热处理后具有以下特点:渗硼层厚度能达到72μm,显微硬度在1248HV_0.1;心部组织为回火马氏体加细小、圆整、均匀分布的碳化物,心部硬度达到62.5HRC;因而能基本满足中小型冷冲压模具对耐磨性和强韧性的要求。（11）GCr15钢经过复合强化热处理后的渗硼层出现少许空洞,没有产生剥落现象,渗硼层过渡比较平缓。把固溶温度由1050℃降到980℃左右,可以达到既能实现固溶的效果,又能克服渗层中的“空洞”现象的目的。（12）T12钢和GCr15钢经过复合强化处理后都具有良好的耐磨性和强韧性,基本能满足中小型冷冲压模具对使用性能的要求,在实际选用中小型模具材料的时候,需要注意以下问题:GCr15钢的淬透性、抗回火性等性能优于T12钢;对于断面尺寸小于30mm、受力较小的小型冷冲压模具,由于受到的压力比较小,淬透性要求不高,因此选用T12钢进行900℃渗硼+四步热处理复合强化处理就能得到较好的效果;对于断面尺寸大于30mm小于45mm、受力稍大的冷冲压模具,可选用GCr15钢进行900℃渗硼+四步热处理复合强化处理。更多还原

【Abstract】 In the course of the use,cold stamping die is subject to the mechanical of compression,shock and friction.Its life is low and the failure performance of it is usually the form of wear,deformation,fracture,etc.So the die material that always choosed high-alloy steel has a complex heat treatment process.To address this issue,the paper analyses the working conditions of cold stamping die.It points out that the main performance requirement should be good enough abrasion resistance and the strength and toughness,etc.So the boronizing process of T12 steel and GCr15 steel is researched,and the effect of carbide ball of conventional ball annealing,recycling the ball annealing,troostite treatment and the four-step heat treatment process is researched,and composite strengthen process,organization and performance of the boronizing + four-step heat treatment was further study, and the mechanism of the boriding and the toughening of steel was analysised. According to analysis and discussion of test results,received the following conclusions:（1）When the boriding temperature is 850℃,boronizing time gradually increase from 1h to 5h,the layer thickness of T12 steel gradually increase from 40μm to 93μm and the layer thickness of GCr15 steel gradually increase from 20μm to 53μm.With the extension of boriding time,the layer thickness also increase, and its increase rate gradually slows down.At the same time,the layer thickness of T12 steel is always higher than GCr15’s.When boronizing time is 5h,boriding temperature gradually increase from 750℃to 950℃,the layer thickness of T12 steel gradually increase from 50μm to 163μm and the layer thickness of GCr15 steel gradually increase from 32μm to 83μm.With the extension of boriding temperature,the layer thickness also increase,and its increase rate gradually speed up.（2）When boronizing time is 5h,boriding temperature gradually increase from 750℃to 900℃,the layer hardness of T12 steel gradually increase from 1155 HV_0.1 to 1216 HV_0.1,and when boriding temperature is 950℃,the layer hardness of T12 steel is 1177 HV_0.1;the layer hardness of GCr15 steel gradually increase from 1147 HV_0.1to 1219 HV_0.1,and when boriding temperature is 950℃,the layer hardness of GCr15 steel is 1163 HV_0.1When the boriding temperature is 850℃,boronizing time gradually increase from 1h to 5h,the hardness of T12 is around 1178HV_0.1～1205HV_0.1,the hardness of GCr15 is around 1178HV_0.1～1205HV_0.1,it indict that boronizing time is less affectedt to the surface hardness of T12 steel and GCr15 steel.（3）After T12 was borided,the surface hardness of T12 is 835HV_0.1,and the sub-surface hardness is 1220HV_0.1,with the layer depth increase,the hardness gradually reduce to matrix-hardness;with the layer depth increase,the hardness of GCr15 also gradually reduce to matrix-hardness,the surface hardness of GCr15 is 835HV_0.1,and the sub-surface hardness is 1220HV_0.1.（4）The junction of the boriding layer and the transition zone is very flat,the contact of the borides and transition zone is few,that is to say the thickness of boride needle inserted into the transitional zone is very shallow（Specially GCr15 steel）,so the binding force of boriding layer and metal matrix is weaken.This will lead to the boriding layer peeling off easily.But there is a concentration gradient of carbon and boron in the transition zone,so lead to the transition zone is gradually excessive to matrix organization.So there is not a clear dividing line between the boriding layer and the transition zone,this make up for these deficiencies,the borides not falling off so easy.（5）The best boronizing process of T12 steel is boriding at 900℃for 5h,layer thickness can be reached 116μm,hardness can be achieved 1216HV_0.1.The best boronizing process of GCr15 steel is boriding at 900℃for 5h,layer thickness can be reached 67μm,hardness can be achieved 1219HV_0.1.This thickness and hardness can meet the requirements.（6）A good effect of micro-carbide is got after T12 steel is carried out carbide micro-technologyl（950℃solution + 700℃high temperature tempering）,the carbide is small,round,evenly distributed;a worse effect of micro-carbide is got after T12 steel is carried out carbide micro-technology 2（950℃solution +760℃ insulation two hours + 690℃insulation 3 hours）,among them,some cusp carbide existence:a worst effect of micro-carbide is got after T12 steel is carried out conventional ball annealing,among them,many large and cusp carbide existence. The quenching and tempering process of four-step heat treatment,troostite heat treatment and conventional heat treatment is 760℃quenching +150℃tempering 60 min.Tempered martensite + carbide can be get.Among them,the carbide of four-step heat treatment is most small,round,evenly distributed.But some cusp carbide is got after T12 steel is carried out troostite heat treatment;many cusp, large carbide is got after T12 steel is carried out conventional heat treatment. Therefore,the strength and toughness after T12 steel carried out four-step heat treatment is better than troostite heat treatment,even better than conventional heat treatment.（7）A good effect of micro-carbide is got after GCr15 steel is carried out carbide micro-technology（950℃solution + 700℃high temperature tempering）, The carbide is small,round,evenly distributed;a worse effect of micro-carbide is got after GCr15 steel is carried out annealing cycle ball,among them,some cusp carbide existence;a worst effect of micro-carbide is got after GCr15 steel is carried out conventional ball annealing,among them,many large and cusp carbide existence.The quenching and tempering process of four-step heat treatment, quenching and tempering after annealing cycle ball and conventional heat treatment is 840℃quenching +150℃tempering 60 min.Tempered martensite + carbide can be get.Among them,the carbide of four-step heat treatmentis most small,round, evenly distributed.But some cusp the carbide is got after GCr15 steel is carried out annealing cycle ball + conventional quenching and tempering,many cusp,large carbide is got after GCr15 steel is carried out conventional heat treatment. Therefore,the strength and toughness after GCr15 steel carried out four-step heat treatment is better than annealing cycle ball + conventional quenching and tempering,even better than conventional heat treatment.（8）T12 steel is carried out compound strengthen heat treatment has the following characteristics:Boriding thickness can reached 120μm,microhardness around in 1235 HV_0.1;the heart organization is tempering martensite and small, round,uniform distribution carbide,and the heart hardness is 61.5 HRC;Thus this is able to meet the small and medium-sized cold stamping die on the strength, toughness and wear-resistance requirements.（9）T12 steel’s Acm is 820℃,when it is borided at 900℃for 5h,carbide decomposition and entered into the austenitic,the carbon atoms proliferate uniform and achieve the result of uniform solution after 5h proliferate,Therefore,the solution temperature is proposed dropped from 950℃to 900℃around. （10）GCr15 is steel carried out compound strengthen heat treatment has the following characteristics:Boriding thickness can reach 72μm,microhardness around in 1248HV_0.1;The heart organization is tempering martensite and small, round,uniform distribution carbide,and the heart hardness is 62.5 HRC;Thus this is able to meet the small and medium-sized cold stamping die on the strength, toughness and wear-resistance requirements.（11）There is a little hollow in the boride layer after GCr15 steel is carried out compound strengthen heat treatment,and there is no spalling phenomenon,boride layer transits relatively smooth.Not only solution can be achieved,but also overcome the phenomenon of layer "hollow",when solution temperature dropps from 1050℃to around 980℃.（12）T12 steel and GCr15 steel are be carried out compound strengthen treatment have good wear resistance and strength and toughness,it can meet the basic performance requirements when cold stamping die is used.In the actual selection the material of small and medium-sized die,it need to pay attention to the following questions:The hardenability and anti-tempering of GCr15 steel is superior than T12 steel;Cold stamping die which size is smaller than 30 mm and subject to smaller force,due to subject to relatively small pressure,don’t need high hardenability,so option T12 steel to make the die,which have a 900℃boronize + four-step heat treatment compound-toughen treatment can be get good effect.Cold stamping die which size is larger than 45 mm not smaller than 30mm and slightly bigger force than the small cold stamping die,relatively slightly bigger pressure, need slightly higher hardenability,so optionl GCr15 steel to make the die,which have a 900℃boronize + four-step heat treatment compound-toughen treatment can be get good effect.更多还原