Forging of 1.9wt%C Ultrahigh Carbon Workroll : Part I - Analysis on Void Formation and Microstructure

Abstract

Compression tests were conducted at the various temperatures and strain rates to investigate void formation and microstructures behavior of a 1.9wt%C ultrahigh carbon steel used in forged workrolls. The microstructure, grain size and volume fraction of cementite were determined using specimens deformed in the temperature range from 800 to 1150 o C and strain rates from 0.01 to 10/s. It was found from the microstructural analysis that the grain size is larger at higher temperatures and lower strain rate deformation conditions. In addition, a higher volume fraction of cementite was measured at lower temperatures. The brittle blocky cementite was fractured at 800 o C and 900 o C regardless of strain rate. As a result, numerous new micro voids were formed in the fragmented blocky cementite. It was also found that local melting can occur at temperatures of more than 1130 o C. Therefore, the forging temperature should be controlled between 900 o C and 1120 o C.The temperature rise, which depends on the anvil stroke and velocity, was estimated through cogging simulation to find the appropriate forging temperature and to prevent local melting due to plastic work.

Microstructures and Crack Formation in Hot Compression Test of Ultrahigh Carbon Steel

“…These voids have to be eliminated by an appropriated process like forging to prevent sudden failure of the forged part in operation. Numerous researchers studied the effects of process parameters on void closure behavior during forging to investigate the relationships among process design, process parameters and behavior of the void closure using the low or middle carbon steel [1][2][3][4][5][6]. It was also revealed from numerical anlyses that hydrostatic pressure and effective strain has a strong influence on the void closure [7][8][9][10][11][12][13].…”