Method for manufacturing equal-hardness CR5 back up roll

A method for manufacturing an equal-hardness Cr5 back up roll, comprising the following steps:

• 1) Preparing steel raw materials according to chemical components in weight percentages for a Cr5 back up roll, and obtaining a steel ingot according to a smelting procedure production process;
• 2) Preparing a roller blank from the steel ingot according to a forging procedure production process;
• 3) Performing thermal treatment on the roller blank;
• and
• 4) Processing and detecting the roller blank to obtain the equal-hardness Cr5 back up roll;
• wherein the thermal treatment of the roller blank in step 3) comprises the following specific steps:
• (1) preheating:
• preheating the processed roller blank in a trolley furnace at a preheating temperature in a range of 400~500° C., and heat-preserving the roller blank for 10~20 h;
• (2) transferring the preheated roller blank into an induction-type differential-temperature quenching device, wherein the induction-type differential-temperature quenching device has a surface temperature measurement precision of 0.1° C. and a surface temperature uniformity of ≤2° C., rapidly heating a steel blank to 950~1,050° C. in the induction-type differential-temperature quenching device at a speed of 15~20° C./min, and heat-preserving the steel blank for 100~150 min;
• (3) transferring the heated roller blank into a quenching device with a continuously controllable cooling speed for quenching, opening a pipeline by adjusting an electromagnetic valve, simultaneously detecting a flow rate and a pressure of the pipeline according to a flowmeter and a pressure gauge respectively, wherein the roller blank is rapidly cooled within an initial 20~30 min, water cooling is used in the rapid cooling stage, the flow rate is controlled to be 300~600 cubic meters/hour, then the flow rate is reduced, and the flow rate is controlled to be 150~250 cubic meters/hour, such that a working layer is a fully quenched martensite structure;
• and
• (4) tempering the quenched roller blank at a tempering temperature in a range of 300~500° C.