The defect in Takata Corp. air bags linked to four deaths in Honda Motor Co. cars opens the supplier to the risk of losing business in a crucial portion of the market for the safety devices.

The market for air bag inflators — the component at the root of deadly defects — is likely to shift away from Takata to suppliers including Stockholm-based Autoliv Inc. and Tokyo-based Daicel Corp.

The two may control more than half the market by 2020 as Takata's share shrinks, said Scott Upham, an analyst who has followed air bags since they were first going into cars a quarter-century ago.