冷作模具钢的切削工艺有哪些？

What are the cutting processes of cold working die steel?

冷作模具钢大多数切削加工都较困难，为了获得良好的切削加工性，需要正确进行热处理，对于表面质量要求较高的模具可选用含S、Ca等元素的易切削模具钢。热处理工艺性主要包括：淬透性、淬硬性、耐回火性、过热敏感性、氧化脱碳倾向、淬火变形和开裂倾向等。下面就来看下冷作模具钢相关知识四个问题吧。

Most cold working die steels are difficult to cut. In order to obtain good machinability, proper heat treatment is required. For dies with high surface quality requirements, free cutting die steels containing s, Ca and other elements can be selected. Heat treatment processability mainly includes: hardenability, hardenability, resistance to reheating, overheating sensitivity, oxidation decarburization tendency, quenching deformation and cracking tendency, etc. Let's take a look at the four problems related to cold working die steel.

什么是冷作模具钢受热软化能力？

What is the heat softening ability of cold working die steel?

受热软化能力反映了冷作模具钢在承载时温升对硬度、变形抗力及耐磨性的影响。表征冷作模具钢受热软化抗力的指标主要有软化温度（℃）和二次硬化硬度（HRC）。咬合抗力实际就是对发生“冷焊”的抵抗能力。

The heat softening ability reflects the influence of temperature rise of cold working die steel on hardness, deformation resistance and wear resistance. Softening temperature (℃) and secondary hardening hardness (HRC) are the main indicators to characterize the thermal softening resistance of cold working die steel. Bite resistance is actually the resistance to "cold welding".

通常在干摩擦条件下，把被试验模具钢试样，与具有咬合倾向的材料（如奥氏体钢），进行恒速对偶摩擦运动，以一定速度逐渐增大载荷，此时转矩也相应增大。当载荷加大到某一临界值时，转矩突然急剧增大，这意味着发生咬合，这一载荷称为“咬合临界载荷”。

Generally, under dry friction conditions, the tested die steel sample and the material with bite tendency (such as austenitic steel) are subject to constant speed dual friction movement, and the load is gradually increased at a certain speed, at this time, the torque is also correspondingly increased. When the load increases to a certain critical value, the torque suddenly increases sharply, which means that the bite occurs. This load is called "bite critical load".

临界载荷越高，标志着咬合抗力越强。冷作模具钢的工艺性能，直接关系到模具的制造周期及制造成本。对冷作模具钢的工艺性能要求，主要有锻造工艺性、切削工艺性、热处理工艺性等。

The higher the critical load, the stronger the bite resistance. The process performance of cold working die steel is directly related to the manufacturing cycle and cost of the die. The process performance requirements of cold working die steel mainly include forging process, cutting process, heat treatment process, etc.

如何提高冷作模具的抗磨性能？

How to improve the wear resistance of cold working dies?

冷作模具在工作时，表面与坯料之间产生许多次摩擦，模具在这种情况下必须仍能保持较低的表面粗糙度值和较高的尺寸精度，以防止早期失效。由于模具材料的硬度和组织是影响模具耐磨性能的重要因素，因此为了提高冷作模具的抗磨性能，通常要求模具硬度高于加工件硬度30%～50%，材料的组织为回火马氏体或下贝氏体，其上分布均匀、细小的颗粒状碳化物。

When the cold working die is working, there are many times of friction between the surface and the blank. In this case, the die must still be able to maintain low surface roughness and high dimensional accuracy to prevent early failure. As the hardness and structure of the die material are important factors affecting the wear resistance of the die, in order to improve the wear resistance of the cold working die, the die hardness is usually required to be 30% ~ 50% higher than the hardness of the machined part. The structure of the material is tempered martensite or lower bainite, on which are evenly distributed and fine granular carbides.

冷作模具的强度指标有哪些？

What are the strength indexes of cold working dies?

强度指标是冷作模具钢设计和材料选择的重要依据，主要包括拉伸屈服点、压缩屈服点等。屈服点是衡量模具零件塑性变形抗力的指标，也是很常用的强度指标。为了获得高的强度，在模具制造过程中，要模具材料的韧性，要根据模具工作条件来决定，对于强烈冲击载荷的模具，如冷作模具的凸模、冷镦模具等，因受冲击载荷较大，需要高的韧性。

Strength index is an important basis for the design and material selection of cold working die steel, mainly including tensile yield point, compressive yield point, etc. Yield point is an index to measure the plastic deformation resistance of mold parts, and it is also a very common strength index. In order to obtain high strength, the toughness of the die material should be determined according to the working conditions of the die in the process of die manufacturing. For dies with strong impact load, such as punch and cold heading dies of cold working dies, due to large impact load, high toughness is required.

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