加热温度对19CrNi5钢组织及硬度的影响

选取轧后硬度高于200 HRB的19CrNi5钢为研究对象,用碳-硅棒箱式高温加热炉将同一炉钢材加热至800、850、900、950、980、1050和1100 ℃,保温40 min后室外15 ℃下空冷,用红外线测温仪测定钢材冷速,并检验钢材硬度、显微组织。经研究,贝氏体是影响钢材硬度的主要原因之一,当加热温度≥1000 ℃,冷速≥2.5 ℃/s时,加热温度越高,冷速越大组织中贝氏体组织比例越大,钢材硬度越高;当加热温度＜1000 ℃,冷速＜1.0 ℃/s时,冷却过程中,奥氏体完全转变为珠光体,最后全部形成珠光体+铁素体组织,钢材硬度低。实际生产中终轧温度控制在1000 ℃以下,冷速＜1.0 ℃/s时,可减缓或消除钢材中贝氏体组织的形成。

Effect of heating temperature on microstructure and hardness of 19CrNi5 steel

The 19CrNi5 steel with hardness higher than 200 HRB after rolling was selected as the research object, the steel specimens were heated to 800, 850, 900, 950, 980, 1050 and 1100 ℃ in the same carbon-silicon rod box-type high temperature furnace. The specimens were hold at the selected temperature for 40 min, then air cooled at 15 ℃,the cooling rate of the steel was measured by infrared thermometer, the hardness was tested by hardness testing device, and the metallographic microstructure of the steel was tested by means of scanning electron microscope(SEM). According to the research results, the main reason is the high proportion of bainite structure that affects the hardness of the steel. When the heating temperature ≥1000 ℃, and the cooling rate ≥2.5 ℃/s, the higher the heating temperature is, the quicker the cooling rate is, the larger the proportion of bainite in the steel is,the higher the hardness of the steel is. When the heating temperature <1000 ℃, cooling rate <1.0 ℃/s, the austenite is completely transformed into pearlite, and finally pearlite and ferrite structure are formed during the cooling process with low hardness of the steel. In actual production, the final rolling temperature is controlled below 1000 ℃, and the cooling rate <1.0 ℃/s, which can slow down or eliminate the formation of bainite structure in the steel.